Aluminum Casting Alloys

ABSTRACT

The invention relates to a light metal alloy.

The invention relates to aluminium casting alloys, in particular for chassis applications. Generally used for this purpose are primarily molten sub-eutectic AlSi alloys which are alloyed with low Mg contents, e.g. AlSi7Mg or AlSi11Mg, to increase the strength. In isolated cases AlSi(Mg, Cu) alloys are also used but these can only have niche applications as a result of the corrosive properties. The same applies to the family of AlCu(Ti, Mg) alloys which offer the highest strengths among the common alloys. Likewise, the AlMg alloys form niche applications in the chassis sector. Other families of alloys such as AlZn or AlLi play no role in chassis.

The components made of the aforesaid alloys are usually subjected to a two-stage heat treatment to achieve the desired properties.

The existing families of alloys generally have the disadvantage that only a limited strength-strain ratio can be achieved thereby. The aforesaid higher-strength alloys with added Cu are frequently eliminated because of the corrosive properties. AlMg alloys are significantly more difficult to pour and therefore are limited in their application (component geometry).

Accordingly, it is the object of the invention to develop an alloy having properties which still have sufficiently high breaking elongation values at high material strengths, particularly for applications in automobile construction. This combination of properties is necessary, for example, in chassis applications in order to be able to withstand cases of abuse. At the same time, the alloy must be sufficiently pourable and should not impose any excessively high requirements on the melting process and the metal cycle on account of their composition.

This is achieved according to the invention by Al casting alloys containing at least five of the following alloying components:

Si: 2.5 to 3.3, preferably 2.7 to 3.1 wt. %

Mg: 0.2 to 0.7, preferably 0.3 to 0.6 wt. %

Fe: <0.18, preferably 0.05 to 0.16 wt. %

Mn: <0.5, preferably 0.05 to 0.4 wt. %

Ti: <0.1, preferably 0.01 to 0.08 wt. %

Sr: <0.03, preferably 0.01 to 0.03 wt. %

Other: <0.1 wt. %

and in each case made up to 100 wt. % with Al.

The alloys according to the invention have a strength-strain ratio which cannot be achieved with conventional Al casting alloys subject to the requirement of freedom from. Cu. In particular, in pressure-assisted casting methods, e.g. low-pressure—back-pressure chill casting, better mechanical technological properties are obtained from the good casting structure.

it can also be advantageous if the alloy is grain-refined.

In order to achieve or further develop the aforesaid advantages, it is advantageous if the cast components are heat-treated, in particular with the following parameters:

Solution annealing: 490 and 540° C. for 1 to 10 h.

Tempering: 150 and 200° C. for 1 to 10 h.

For some applications, however, it can also be advantageous if only one single-stage tempering treatment is carried out, generally known as, for example, T4, T5 or 0.

In addition to the aforesaid advantages exhibited by components of alloys according to the invention, it is additionally found that as a result of the lack of Cu and Cn alloying constituents, the corrosion resistance is increased significantly. The product is also relatively inexpensive because none of the alloying additions such as, for example, rare earth metals which make the product more expensive are used, the usual melting treatment can be used and no particular expenditure is required for separating circuits.

An excellent strength-strain ratio is also provided with excellent pourability. Firstly, the pourability makes it possible to achieve a casting free from major defects, known as blow holes and secondly, the microstructure is positively influenced in such a manner that the number of internal notches which reduce the breaking elongation is kept as low as possible.

The following may be given as example values:

R_(m) R_(p 0.2) A₅ [MPa] [MPa] [%] Gravitational chill casting 250 140 13 Casting state Gravitational chill casting 320 260 5 Heat treatment T6 (540° C., 7 h, 160° C., 8 h) Pressure-assisted chill casting 370 300 11 Heat treatment T6 (540° C., 7 h/160° C., 6 h) *only give the precise values when absolutely necessary 

1. An Al casting alloy containing at least five of the following alloying components: Si: 2.5 to 3.3, preferably 2.7 to 3.1 wt. % Mg: 0.2 to 0.7, preferably 0.3 to 0.6 wt. % Fe: <0.18, preferably 0.05 to 0.16 wt. % Mn: <0.5, preferably 0.05 to 0.4 wt. % Ti: <0.1, preferably 0.01 to 0.08 wt. % Sr: <0.03, preferably 0.01 to 0.03 wt. % <0.03 wt. % Other: <0.1 wt. % and in each case made up to 100 wt. % with Al.
 2. The Al casting alloys according to claim 1, wherein the parts cast therefrom are solution-annealed between 490 and 540° C. for 1 to 10 h.
 3. The Al casting alloys according to claim 1, wherein the parts cast therefrom are tempered between 150 and 200° C. for 1 to 10 h.
 4. The Al casting alloys according to claim 1, wherein the alloys are grain-refined.
 5. Use of Al casting alloys according to claim 1, wherein component or parts for respectively chassis part of motor vehicles. 